There is no settled science. You can ask any mushroom hunter those questions and you'll get completely different answers. I'm from the school of consider everything, try as much as you can.
I've read books by expert morel hunters that say once your daytime temps stay in the low 60's for 5 days straight, it's time to start looking. What I would add, is that soil temp has to be there as well. Make sure it hasn't froze for at least a week before you go.
Where? Any place you find trees that are in some phase of dying or have died recently. The morels feast on the decaying roots of almost any silver barked deciduous tree. There is a pecking order among the favorites.
1. Elms (look for bark peeling off in vertical sheets, exposing then a smooth surfaced wood core)
2. Apples
3. Cherries
4. Everything else
A good rain is a huge help. Most of the midwest is going to get good rain this week. Once that happens, a few days of heat and I say it's gonna be on. I'm on the MN/IA border, and if we can get some heat, It'll start within two days of that.
I focus on checking lots of places. Give each spot a minute or two. If there is any sort of quantity there, you'll at least see one of them. If not, keep moving and keep looking. Once you see one, STOP! Do not move. Look at every step you take from there because you'll start stepping on them if you just run up to it. Get low and quiet and start harvesting.
And take pictures!
